Monday, January 12, 2015

More Testing on Work-Hardening Sterling Silver



In my last blog post I wrote about how fine silver cannot be work-hardened. I also listed a method of work-hardening sterling silver by heating it in a kiln:
 
Step 1: Check the sterling for any solder joints that may already be present.

Step 2: Heat the sterling to 1292°F–1346°F (700°C–730°C) for 30–60 minutes; adjusting temperatures if solder is present (if low-temperature solder is present, heat the piece only to 1000°F–1200°F). Quench in water.

Step 3: Heat the sterling again, this time to 572°F (300°C), holding at that temperature for 30–60 minutes. After cooling, Vickers hardness will range between 120–140dph; if lower temperatures are used, the sterling will not achieve this level.
 

Someone asked me a great question, "if sterling silver turns brittle after heating it above 1300°F, why would this procedure not make the sterling silver brittle? Isn't this what we have all been taught, to not heat above 1300°F?" I set out to test the technique. 

Test 1
I heated a strip of sterling silver sheet to the highest temperatures in the above steps. First, to 1346°F (730°C) and held it for 60 minutes. I allowed the oven to cool a bit, and then I quenched the metal. I then re-heated it to 572°F (300°C), held the temperature and then allowed it to air cool. The results, very hard sterling silver sheet and not brittle!

Test 2
I heated another strip of sterling silver sheet to the lowest temperature 1292°F (700°C), held it for 60 minutes, allowed the oven to cool a bit, and then quenched the metal. I then re-heated it to 572°F (300°C) holding the temperature and then allowed it to air cool. The results, very hard sterling silver sheet and not brittle!

So, my next question is, "At what temperature does the sterling silver metal become brittle?"

I will continue my testing and report back!

Until next time, have fun claying around!





 
by Janet Alexander 
Technical Adviser

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